Bjørn Molt Petersen

Evaluating nitrogen taxation scenarios using the dynamic whole farm simulation model FASSET

The whole farm model FASSET ver. 1.0 was used for evaluation of the environmental and economic consequences of implementing different nitrogen taxes. The taxation policies analysed were a tax on nitrogen in mineral fertiliser, a tax on nitrogen in mineral fertiliser and imported animal feedstuff, and a tax on the farm nitrogen surplus. In these scenarios, the tax price was equal to the price of the nitrogen in mineral fertilisers (0.67 E kg N 1 ). Four farm types were considered: arable on sandy soil, arable on loamy soil, pig production on sandy soil and pig production on loamy soil. Impacts of the taxes for each farm type on crop rotation, fertiliser use and pig production were estimated by the Linear Programming module of FASSET. The dynamic simulation module of FASSET evaluated the environmental and economic consequences of the new production plans. The social abatement cost of reducing nitrate leaching varied between 1 and 9 E kg N 1 . None of the taxation policies was the most cost-effective for all farm types. Tax on mineral fertiliser favours pig producers, whereas the tax on nitrogen surplus favours arable farms. Thus efficient taxation schemes for reduction of nitrate leaching should differentiate between farm types rather than use uniform input taxes. # 2003 Elsevier Science Ltd. All rights reserved.

Environmental Consequences of Future Biogas Technologies Based on Separated Slurry

This consequential life cycle assessment study highlights the key environmental aspects of producing biogas from separated pig and cow slurry, a relatively new but probable scenario for future biogas production, as it avoids the reliance on constrained carbon cosubstrates. Three scenarios involving different slurry separation technologies have been assessed and compared to a business-as-usual reference slurry management scenario. The results show that the environmental benefits of such biogas production are highly dependent upon the efficiency of the separation technology used to concentrate the volatile solids in the solid fraction. The biogas scenario involving the most efficient separation technology resulted in a dry matter separation efficiency of 87% and allowed a net reduction of the global warming potential of 40%, compared to the reference slurry management. This figure comprises the whole slurry life cycle, including the flows bypassing the biogas plant. This study includes soil carbon balances and a method for quantifying the changes in yield resulting from increased nitrogen availability as well as for quantifying mineral fertilizers displacement. Soil carbon balances showed that between 13 and 50% less carbon ends up in the soil pool with the different biogas alternatives, as opposed to the reference slurry management.

Comparison of methods for simulating effects of nitrogen on green area index and dry matter growth in winter wheat

Abstract Crop simulation models are increasingly being used to simulate the response of crop production to variation in input use. Current and widely used crop models differ strongly in the way in which green area index (GAI) and radiation use efficiency (RUE) is affected by nitrogen (N) supply. Three different methods of simulating effect of N on development of GAI were tested in combination with three different methods of simulating effects of N on RUE. The methods tested represent functions applied in three existing wheat simulation models: FASSET, Sirius and DAISY. GAI depends in FASSET on crop dry weight, temperature and N uptake, in Sirius on temperature and N uptake, and in DAISY GAI depends on dry weight and temperature. Sirius has no effect of N on RUE, DAISY uses a segmented linear response function, and FASSET uses a curvilinear response. The different methods were implemented in the FASSET model framework, and maximum RUE at optimal N supply was calibrated for each model combination using 4 years of growth analysis data from an experiment in winter wheat with three rates of mineral N fertiliser at Research Centre Foulum, Denmark. The model combinations were validated using 2 years of growth analysis data from an experiment at Research Centre Foulum with different timing of N application. The model combinations were tested against grain yield response to increasing N supply from a series of N fertiliser experiments in Denmark. The observed development of GAI and dry weight over time in the calibration and validation data sets could be reproduced by all combinations of GAI and RUE models. This shows that a large variation in N supply rates is more important than detailed sampling over time when validating and testing crop response to N supply. The observed response of grain yield to increasing rates of mineral N fertiliser could be reproduced by most of the model combinations. However, the yield increase was overestimated with the use of a segmented linear response of RUE to N supply, and the optimal N rate was underestimated when the N response of RUE was ignored.

Modelling the carbon and nitrogen balances of direct land use changes from energy crops in Denmark: a consequential life cycle inventory

This paper addresses the conversion of Danish agricultural land from food/feed crops to energy crops. To this end, a life cycle inventory, which relates the input and output flows from and to the environment of 528 different crop systems, is built and described. This includes seven crops (annuals and perennials), two soil types (sandy loam and sand), two climate types (wet and dry), three initial soil carbon level (high, average, low), two time horizons for soil carbon changes (20 and 100 years), two residues management practices (removal and incorporation into soil) as well as three soil carbon turnover rate reductions in response to the absence of tillage for some perennial crops (0%, 25%, 50%). For all crop systems, nutrient balances, balances between above‐ and below‐ground residues, soil carbon changes, biogenic carbon dioxide flows, emissions of nitrogen compounds and losses of macro‐ and micronutrients are presented. The inventory results highlight Miscanthus as a promising energy crop, indicating it presents the lowest emissions of nitrogen compounds, the highest amount of carbon dioxide sequestrated from the atmosphere, a relatively high carbon turnover efficiency and allows to increase soil organic carbon. Results also show that the magnitude of these benefits depends on the harvest season, soil types and climatic conditions. Inventory results further highlight winter wheat as the only annual crop where straw removal for bioenergy may be sustainable, being the only annual crop not involving losses of soil organic carbon as a result of harvesting the straw. This, however, is conditional to manure application, and is only true on sandy soils.

Estimated N leaching losses for organic and conventional farming in Denmark

The impact of organic compared to conventional farming practices on N leaching loss was studied for Danish mixed dairy and arable farms using an N balance approach based on representative data. On mixed dairy farms a simple N balance method was used to estimate N surplus and N leaching loss. On arable farms the simple N balance method was unreliable due to changes in the soil N pool. Consequently, the FASSET simulation model was used to estimate N surplus, N leaching loss and the changes in the soil N pool. The study found a lower N leaching loss from organic than conventional mixed dairy farms, primarily due to lower N inputs. On organic arable farms the soil N pool was increasing over years but the N leaching loss was comparable to conventional arable farms. The soil N pool was primarily increased by organic farming practices and incorporation of straw. The highest increase in the soil N pool was seen on soils with a low level of soil organic matter. The level of N leaching loss was dependent on soil type, the use of catch crops and the level of soil organic matter, whereas incorporation of straw had a minor effect. N leaching was highest on sandy soils with a high level of soil organic matter and no catch crops. The study stresses the importance of using representative data of organic and conventional farming practices in comparative studies of N leaching loss.

Developments in greenhouse gas emissions and net energy use in Danish agriculture – How to achieve substantial CO2 reductions?

Greenhouse gas (GHG) emissions from agriculture are a significant contributor to total Danish emissions. Consequently, much effort is currently given to the exploration of potential strategies to reduce agricultural emissions. This paper presents results from a study estimating agricultural GHG emissions in the form of methane, nitrous oxide and carbon dioxide (including carbon sources and sinks, and the impact of energy consumption/bioenergy production) from Danish agriculture in the years 1990-2010. An analysis of possible measures to reduce the GHG emissions indicated that a 50-70% reduction of agricultural emissions by 2050 relative to 1990 is achievable, including mitigation measures in relation to the handling of manure and fertilisers, optimization of animal feeding, cropping practices, and land use changes with more organic farming, afforestation and energy crops. In addition, the bioenergy production may be increased significantly without reducing the food production, whereby Danish agriculture could achieve a positive energy balance.

Impact of organic pig production systems on CO2 emission, C sequestration and nitrate pollution

Organic rules for grazing and access to outdoor areas in pig production may be met in different ways, which express compromises between considerations for animal welfare, feed self-reliance and negative environmental impact such as greenhouse gas emissions and nitrate pollution. This article compares the environmental impact of the main organic pig systems in Denmark. Normally, sows are kept in huts on grassland and finishing pigs are raised in stables with access to an outdoor run. One alternative practice is also rearing the fattening pigs on grassland all year round. The third method investigated was a one-unit pen system mainly consisting of a deep litter area under a climate tent and with restricted access to a grazing area. Using life cycle assessment (LCA) methodology, the emissions of greenhouse gases of the free range system were estimated to be 3.3 kg CO2-equivalents kg−1 live weight pig, which was significantly higher than the indoor fattening system and the tent system, yielding 2.9 and 2.8 kg CO2-eq. kg−1 pig, respectively. This was 7–22% higher compared with Danish conventional pig production but, due to the integration of grass-clover in the organic crop rotations these had an estimated net soil carbon sequestration. When carbon sequestration was included in the LCA then the organic systems had lower greenhouse gas emissions compared with conventional pig production. Eutrophication in nitrate equivalents per kg pig was 21–65% higher in the organic pig systems and acidification was 35–45% higher per kg organic pig compared with the conventional system. We conclude that, even though the free range system theoretically has agro-ecological advantages over the indoor fattening system and the tent system due to a larger grass-clover area, this potential is difficult to implement in practice due to problems with leaching on sandy soil. Only if forage can contribute to a larger proportion of the pigfeed uptake may the free range system be economically and environmentally competitive. Improvement of nitrogen cycling and efficiency is the most important factor for reducing the overall environmental load from organic pig meat. Presently, a system with pig fattening in stables and concrete-covered outdoor runs seems to be the best solution from an environmental point of view.

Simulating soil N2O emissions and heterotrophic CO2 respiration in arable systems using FASSET and MoBiLE-DNDC

Modelling of soil emissions of nitrous oxide (N2O) and carbon dioxide (CO2) is complicated by complex interactions between processes and factors influencing their production, consumption and transport. In this study N2O emissions and heterotrophic CO2 respiration were simulated from soils under winter wheat grown in three different organic and one inorganic fertilizer-based cropping system using two different models, i.e., MoBiLE-DNDC and FASSET. The two models were generally capable of simulating most seasonal trends of measured soil heterotrophic CO2 respiration and N2O emissions. Annual soil heterotrophic CO2 respiration was underestimated by both models in all systems (about 10–30% by FASSET and 10–40% by MoBiLE-DNDC). Both models overestimated annual N2O emissions in all systems (about 10–580% by FASSET and 20–50% by MoBiLE-DNDC). In addition, both models had some problems in simulating soil mineral nitrogen, which seemed to originate from deficiencies in simulating degradation of soil organic matter, incorporated residues of catch crops and organic fertilizers. To improve the performance of the models, organic matter decomposition parameters need to be revised.

A flexible tool for simulation of soil carbon turnover

Abstract Existing models of soil organic matter (SOM) turnover are implemented within rigid and often complex modelling environments, which makes the testing of influence of SOM model structure a rather difficult task. A new soil carbon turnover simulation tool is presented ( c-tool v. 1.0). It facilitates the construction of a wide range of user-definable SOM models based on linked SOM pools and a decay described for each pool by first order kinetics. Simulation of carbon isotopes 13C and 14C is facilitated. No programming is necessary for defining or redefining models, as the model structure is given in set-up files. The program is fast, and can utilise a range of time-steps, which enhances the computation of steady level SOM contents. The ability of c-tool to mimic and analyse an existing model was tested using the daisy SOM-model as an example. It was found that both the reduction of the vertically layered SOM-model in daisy to one layer, and the exclusion of C/N interactions only had small effects on the simulated development in soil carbon content during a 30-year period. This suggests that C/N interactions and vertical layering may initially be ignored when constructing and calibrating models for SOM turnover, which reduces model complexity and input demands considerably. The steady level carbon content was simulated for two soils and a range of management types. An analysis of the models sensitivity in simulated steady level carbon content to variation in carbon-input and key parameters was performed, and simulated isotope tagging was demonstrated as a powerful method for analysing carbon flows.

Cortical Plasticity after Cochlear Implantation

The most dramatic progress in the restoration of hearing takes place in the first months after cochlear implantation. To map the brain activity underlying this process, we used positron emission tomography at three time points: within 14 days, three months, and six months after switch-on. Fifteen recently implanted adult implant recipients listened to running speech or speech-like noise in four sequential PET sessions at each milestone. CI listeners with postlingual hearing loss showed differential activation of left superior temporal gyrus during speech and speech-like stimuli, unlike CI listeners with prelingual hearing loss. Furthermore, Brocas area was activated as an effect of time, but only in CI listeners with postlingual hearing loss. The study demonstrates that adaptation to the cochlear implant is highly related to the history of hearing loss. Speech processing in patients whose hearing loss occurred after the acquisition of language involves brain areas associated with speech comprehension, which is not the case for patients whose hearing loss occurred before the acquisition of language. Finally, the findings confirm the key role of Brocas area in restoration of speech perception, but only in individuals in whom Brocas area has been active prior to the loss of hearing.